The liminal brightness increment as a function of wave-length for different conditions of the foveal and parafoveal retina

Abstract

In this paper will be given the results of measurements of the least perceptible difference of brightness between a test patch and its immediate surrounds, the difference of brightness being produced by monochromatic light of various wave-lengths throughout the spectrum. Observations have been made both for foveal and 5°-parafoveal vision of the test spot, and with the eye in various conditions of adaptation. In the early studies of the brightness difference threshold (b. d. t.), for example in König and Brodhun's (1903) classical research, the subject viewed a photometric field of the same colour (spectral composition) throughout, but divided into two halves whose brightnesses where adjusted to the critical difference.